178 



ZOOLOGY 



SECT. 



closed by membrane, one of them of great size in Callorhynchus. 

 The skeleton of the anterior clasper articulates with the pubic 

 region. 



Digestive Organs. The teeth (Fig. 802) are very character- 

 istic, having the form of strong plates with an irregular surface 

 and a sharp cutting edge. In the upper jaw there is a pair of 

 small vomerine teeth (vo. t.) in front, immediately behind them 

 a pair of large palatine teeth (pal. t.\ and in the lower jaw a single 



6.0 



t/o.l 



oc.cn 



FIG. 802. Callorhynchus antarcticus, sagittal section of skull ; the labial cartilages are- 

 removed, a. s. c. apertures through which the anterior semicircular canal passes from the 

 cranial cavity into the auditory capsule ; e. 1. <L aperture for endolymphatic duct ; mck. c. 

 Meckel's cartilage ; mnd. t. mandibular tooth ; nch. notochord ; JVV. 5, trigeminal foramen ; 

 NV. 5. o. foramen for exit of ophthalmic nerve; Nr. o.'o', canal for ophthalmic nerves with 

 apertures of entrance and exit ; Nv. 10, vagus foramen ; oc. en. occipital condyle ; or. 

 fenestra separating cranial cavity from orbit ; pal. qu. palato-quadrate ; pal. t. palatine tooth ; 

 pn. position of pineal body ; pt. pit for extra-cranial portion of pituitary body ; p. .<*. c. apertures 

 through which the posterior semicircular canal passes into the auditory capsule ; qu. quadrate 

 region of palato-quadrate ; '/. rostrum ; sac. depression for sacculus ; s. t. sella turcica ; tr. 

 tritor ; ro. t. vomerine teeth. 



pair of large mandibular teeth (mncl.t.). They are composed of vaso- 

 dentine, and each palatine and mandibular tooth has its surface 

 slightly raised into a rounded elevation of a specially hard sub- 

 stance, of whiter colour than the rest of the tooth, and known 

 as a tritor (tr). The stomach is almost obsolete, the enteric canal 

 passing in a straight line from gullet to anus ; there is a well- 

 developed spiral valve in the intestine. 



Respiratory Organs.- -There are three pairs of holobranchs or 

 complete gills borne on the first three branchial arches, and two- 



